Conventional single crystal diamond semiconductor films can be manufactured by the method of generating microwave plasma, and thus growing a diamond film which includes carbon and phosphorous on a heated diamond substrate within a vacuum container into which a gas including hydrogen, carbon and phosphorous atoms has been introduced (Patent Document 1). Here, it is described that “In order to grow a single crystal diamond film, it is desirable to use heteroepitaxially grown diamond or a single crystal diamond substrate. Though any of the (111) plane, the (110) plane or the (100) plane may be used, the (111) plane is desirable,” and according to the document, a film of n type (111) oriented single crystal diamond semiconductor doped with phosphorous atoms is fabricated using the (111) plane of a diamond crystal in an embodiment, and the generation thereof is confirmed. Furthermore, in the disclosed scope of the invention, there is a description that this invention can be practiced in a region where the ratio of the number of atoms for P/C of P in phosphine PH3 to C of methane CH4 is such that P/C≦4% and the ratio of the number of atoms for C/H of C in CH4 to H of hydrogen H2 is such that C/H≦1%, and that n type (111) oriented single crystal diamond semiconductor, which are examples for defining the scope of the invention and designated as • in FIG. 1, can be formed. Meanwhile, it is described that in comparative examples designated as x it cannot be obtained on the (111) plane.
Concerning this, the inventors published some information similar to the above (Non-patent Documents 1 and 2).
However, as far as the present inventors know, there are no preceding examples that confirmed the existence of an n type diamond semiconductor on the (100) plane in any patent or academic paper. In addition, there is a reported example that no n type diamond semiconductor grew on the (100) plane under the synthesis conditions on the (111) plane (Non-patent Document 4). As described above, conventional n type diamond semiconductors have been obtained only with a particular ratio of the number of atoms only on the (111) plane. Even when such methods are attempted, however, a film of n type (100) oriented single crystal diamond semiconductor, which is important in the industry, could not be obtained, due to poor reactivity.
There was attempt to manufacture films of (100) oriented single crystal diamond semiconductor which allow provision of an enlarged area and flattening through polishing relatively easily, and low interface state density, which are suitable for semiconductor devices, compared with diamond substrates having a (111) substrate. The ratio of phosphorous atoms to carbon atoms in the gas which is used as a raw material, however, is at a level of approximately several tens of ppm to several thousands of ppm at the highest. This is because it was firmly believed that increase in the amount of n type atoms added to be harmful to the crystallinity of the fabricated n type diamond semiconductor single crystal film.
For example, in preparing p type diamond semiconductors, diborane B2H6 is used as an acceptor, but also it has been carried out with a ratio B/C of diborane to CH4 of approximately several tens of ppm to several thousands of ppm. Though there are rare examples of experiments being conducted with a concentration of as high as 2000 ppm (Non-patent Document 3), the ratio in these is 0.2% at the highest. The crystallinity of diamond becomes poor when the concentration is further increased.
The n type (100) oriented single crystal diamond semiconductor, in particular, can show properties that provision of an enlarged area and flattening through polishing are relatively easy and the interface state density is low, and thus the (100) oriented single crystal diamond films are thus suitable for devices and have high utility value. However, n type conduction on (100) oriented diamond could not be attained substantially.    Non-patent Document 1: S. Koizumi et al., Appl. Phys. Lett., 71, 1065 (1997)    Non-patent Document 2: S. Koizumi et al., Diamond and Related Materials, 9, 935 (2000)    Non-patent Document 3: K. Ushizawa et al., Diamond and Related Materials, 7, 1719 (1998)    Non-patent Document 4: M. Nesladek, Semicond. Sci. Technol., 20, R19 (2005)